Structural behavior of welded H-sections made of high-strength S690 steel plates and their applications in construction

This chapter presents a comprehensive experimental and numerical investigation into the structural behavior of both stocky and slender columns of the high-strength S690 welded H-section under axial compression. These members were expected to behave in an essentially similar fashion to those columns of the normal-strength S355 welded section columns, and a total of 24 axial compression tests on both stocky and slender columns have been conducted. This has permitted the specific effects of initial imperfections, namely, (1) welding-induced residual stresses and (2) member out-of-straightness, accurately on the structural behavior of these particular sections under axial compression to be assessed. The effects of residual stresses on the deformation characteristics of these S690 welded sections are generally considered to be proportionally less pronounced than is the case for S355 welded sections. Hence, an improvement to the current design rules recommended in EN 1993-1-1 is highly desirable. To develop representative numerical models that simulate the structural behavior of these S690 welded H-sections with an accurate incorporation of the welding-induced residual stresses, an integrated numerical modeling technique for the thermal, thermomechanical, and structural responses of these high-strength S690 welded H-sections has been developed. Compatible three-dimensional finite element models with both heat transfer and stress elements are employed to perform sequentially coupled thermomechanical analyses, followed by structural analyses. Through a rational simulation of the welding process, highly nonlinear welding-induced residual stresses in the vicinity of the flange/web junctions are fully incorporated into the structural models of these welded H-sections together with geometrical initial imperfections when examining the structural behavior of both stocky and slender columns under axial compression. These models have been carefully calibrated against transient surface temperature histories during welding, surface residual stresses after welding, and deformation characteristics under axial compression. A comprehensive parametric study was then performed to generate a total of 80 numerical data that served as the basis for a rational improvement to the current design rules given in EN 1993-1-1, using suitably selected material-dependent parameters.